Underwater storage reservoir



April 15, 1969 J. M. CLEARY UNDERWATER STORAGE RESERVOIR Sheet FiledOct. 9, 1967 INVENTbR. James M. Cleory April 15, 1969 J. M. CLEARYUNDERWATER STORAGE RESERVOIR Z of 2 Sheet Filed Oct. 9, 1967 lN\/'E1ITOR. James M. Cleory m w FE w w @MJM Attorney United States ABSTRACT OFTHE DISCLOSURE Offshore underwater storage is created by forming a pileof objects heavier than water on the bottom of a body of water and byforming a thick impermeable upper barrier, preferably moldable, coveringand supported by the pile. Two or more conduits are placed in the pile.A water-immiscible liquid lighter than water is added to, stored in andremoved from the pile. The objects for the pile are preferablytransported over water to location and may be deposited on a previouslyformed impermeable lower barrier. Pumping liquid from the pileconsolidates the upper barrier and pile. Heavy material may be spreadover the upper barrier. The pressure inside the pile may be maintainedlower than water pressure on the upper barrier.

Background of the invention This invention pertains to a method offorming an underwater storage reservoir and of storing a waterimmiscibleliquid having a specific gravity less than water in the storagereservoir.

There is a need for a less expensive, easy and quick way to constructlarge hydrocarbon storage reservoirs in offshore oil producing areas.The storage requirement for offshore production is very large. Standardoffshore production practice requires a minimum storage capacity of tendays production and even greater storage volumes are required in theless accessible offshore producing areas. In order to be economical,offshore fields are generally produced at very high daily rates;consequently, a storage volume holding ten or more days production caninvolve hundreds of thousands to millions of barrels of storagecapacity. In addition, in offshore areas where the oil is produced tostorage to later be transferred to a tanker, the storage volume shouldbe at least as great as the capacity of the tanker, A common guide forestablishing the capacity of storage for tankers is to have enoughcapacity to fill the tanker plus five days production. A small T2 tankerholds 120,000 barrels and five days production would be likely torequire an additional one hundred thousand barrels. Tankers having acapacity of over a million barrels are already in use and tankersholding several million barrels are soon to be used.

The most accepted method of providing large storage capacities is toprovide tanks on short and pipeline the oil to these tanks. Thisconventional method requires a long time to construct, is most expensiveand involves the many problems related to coastal land use. Rigid tanksalso have a maximum practical size limited by the strength of largesections of the rigid tank materials and the inability to handle andtransport these large rigid sections; consequently, the cost per barrelof storage does not decline as the size of the storage facility isincreased beyond this maximum practical size.

The increase in size of tankers has created a further limitation to theuse of onshore storage. Many waterways cannot handle the new largetankers. In such areas, it is necessary to build an offshore island orloading dock in water suitable for these large tankers.

atent O "ice Various types of offshore storage facilities have beenproposed. For example, it has been proposed to use cement or steel tanksweighted by sand or rock, and to use flexible bagsmoored to the oceanfloor, and to use anchored tankers or floating tanks. Most of theseproposals are not feasible for anything but small amounts of hydrocarbonstorage. It would be feasible to use a large tanker as a storagefacility, but the expected cost per barrel of such storage would exceedtwelve dollars and there are many risks to this type of offshore storagewhich are not justified in view of the already high cost per barrel ofstorage. Providing mooring and piping to these large floating tankersposes additional problems.

Offshore submerged storage facilities involve other unique design andoperational problems. There are several sources of stress on the wallsand roof of the submerged storage reservoir. These stresses vary indirection and magnitude. There are buoyant forces inside the storagereservoir created by the oil being lighter than water and the fact thatthe oil in the storage reservoir to tensile stresses. An opposite orcompressive stress is created when the storage reservoir is unloadedbecause, in order to minimize tanker loading time, storage reservoirsare unloaded at a rate sufiicient to collapse the walls of a rigid tank.Thus, the walls of the underwater storage reservoir undergo cycliccompressive and tensile forces which expand and contract the walls ofthe storage reservoir. These cyclic forces fatigue rigid materials. Itshould be noted that standard methods of ballasting tanks do notovercome the effects of these cyclic forces. It would, therefore, bebeneficial to provide a submerged storage container that will eitherwithstand both compressive and tensile forces, or in the alternative,one that is operated in a manner to avoid the effects of one or more ofthe forces.

In addition to the tensile and collapsed forces just described,submerged storage reservoirs must withstand large water thrusts orscouring action which forces vary in direction and magnitude. Thesewater forces peak when there is storm at sea and standard storagereservoirs are designed for the largest peak forces since there is noready way to increase the resistance to wave action for only the shortpeak periods. It would be additionally advantageous if the design of thestorage reservoir were such as to better withstand Water thrusts and ifthe strength and stability of the storage reservoir could be increasedduring periods of peak wave forces.

Under normal operating conditions, oil will leak from a submerged orsubstantially submerged tank into the Water and it is difficult torepair the leak as long as oil is present. It would be advantageous ifthe storage reservoir could be operated in a manner that avoids leakageinto the water and at the same time permits ready repair of the leakWhile oil is being stored.

When a tanker ties up to a submerged storage reservoir to load, theremust be provided a secure way of mooring the tanker. It would beadvantageous if the storage reservoir could also act as a stable mooringfor the tanker or a loading platform.

Offshore reservoirs should be easy to construct and made of materialsthat can be handled and shipped in large quantities and that are readilyavailable in most areas. Offshore reservoirs should also be near theproducing wells.

Accordingly, there is a genuine need for a method of constructing andoperating a large offshore storage facility.

Summary of the invention This invention provides a method of creatingand operating an offshore, underwater storage reservoir forwater-immiscible liquids having a specific gravity less than water. Thelight, water-immiscible liquid is stored in the voids of a pile of highbulk porosity objects which in addition to supplying the storage volumealso provides support and stability to the reservoir. The systemprovided herein is chiefly noted for its ease of construction,practically unlimited size, ruggedness and applicability to any depthWater.

The underwater storage reservoir is created by forming a pile of highbulk porosity on the bottom of a body of water with the top of the pilebeing below the surface of the water. The pile is composed of a quantityof objects heaped together in multiple vertical and horizontal layersthereby providing a pile having an upper portion and a lower portion.The objects are composed of material having a density greater than thedensity of water. For example, oyster shells, large sized heavy objectssurrounded by finer objects, or large sized rocks having a size at leastas great as 0.5 foot. A thick upper barrier being suflicientlyimpermeable to contain the water-immiscible liquid within the pile isformed over and supported by the pile. At some time during constructionof the storage reservoir, a minimum of two flow conduits are placed in amanner such that when the storage reservoir is completed the fiowconduits extend from inside the pile to outside the upper barrier withone conduit in communication with the upper portion of the pile and theother conduit in communication with the lower portion of the pile.Usually, an impermeable lower barrier will be formed over a portion ofthe bottom of the sea and the pile formed on top of this lower barrier.Preferably, the objects for the pile will be transported to location anddeposited either on the sea bottom or the lower barrier. It is alsopreferred that the upper barrier over the pile be moldable. The upperbarrier, the pile and the bottom of the body of water beneath the pilemay be consolidated by pumping liquid from beneath the upper barrier ata rate sufiicient to reduce the pressure inside the pile. A materialheavier than water may be spread over the top of the upper barrier. Thisheavy material may be large sized objects or layers of small sizedobjects covered with larger sized objects. The top of the heavy materialmay be above water; however, the top will usually be below the surfaceof the water. The amount of heavy material may be suflicient to place anet downward force on the exterior of the upper barrier. Awater-immiscible liquid lighter than water is added to the pile tooccupy the upper portion of the pile. A portion of this water-immiscibleliquid is later removed. An especially unique feature of this storagesystem is that the pressure of the stored liquid inside the storagereservoir with or without heavy material over the upper barrier may bemaintained lower than the water pressure on top of the upper barrier forany predetermined period without collapsing the storage reservoir. Thispressure reduction greatly improves the sta bility and operation of thestorage system. For example, a lower pressure inside the storagereservoir may be maintained when water-immiscible liquid is being addedto the pile, or whenever wave action is likely to damage the pile, orwhen a tanker is loading from the pile, or when a leak develops, orthroughout an entire storage cycle.

The foregoing summary and the following description show that thisinvention provides a new, less expensive method for constructing andoperating a large, rugged, submerged storage reservoir. The storagereservoir is made up of common, readily available materials and isconstructed in a manner such that the size of the storage reservoir ispractically unlimited and the cost per barrel of storage declines as thesize of the storage reservoir is increased. Moreover, the storagereservoir may be constructed in any depth water so as to be readilyaccessible to large tankers or to be adjacent production equipment.

Brief description of drawings Description of the preferred embodimentsThis invention pertains to a method of forming and operating anunderwater storage reservoir. The drawings are designed to assistdescription of the method of constructing and operating this underwaterstorage system and are neither to scale nor exact in detail. In thefigures, similar items have the same reference numeral and the featuresof any one figure could be used in any other figure when desired.

The underwater storage system is for storage of a waterimmiscible liquidhaving a specific gravity less than the water in which the light,water-immiscible liquid is stored. For purposes of description, thislight liquid is herein also referred to as crude oil or oil and the bodyof water in which the oil is stored is also called sea water or the sea.

As illustrated in the drawings, the storage system is made by formingpile 11 on bottom 13 of body of water 15 with the top of the pile beingbelow surface 17 of the body of water as shown in FIGURE 1, or on lowerbarrier 19 as shown in FIGURE 3. Lower barrier 19 is formed by coveringa substantially greater portion of the bottom of body of water than isto be covered by the storage reservoir. The pile would then be formed ontop of this lower barrier. Lower barrier 19 is designed to besubstantially impermeable and to greatly improve operation of thestorage system especially that part of the storage method which relatesto a reduction in pressure inside of the pile as hereinafter described.It is essential that pile 11 be supported by the sea floor. This isaccomplished by forming the pile either on the sea floor or on somethingsupported by the sea floor, e.g., the lower barrier. If the sea floor isstable and sufficiently level, the lower barrier may be formed simply ofconcrete poured on the sea fioor. Usually, however, the sea floor willsettle and it is much preferred that the lower barrier be flexible andmoldable for reasons hereinafter explained in conjunction with an upperbarrier placed over the pile. In such case, the lower barrier will bemade of similar materials as the upper barrier.

Pile 11 is composed of a quantity of objects heaped together in multiplehorizontal and vertical layers thereby providing the pile with upperportion 21 and lower portion 23 The objects are chunks, lumps, pieces,rubble, scrap or other loose objects. The objects are composed ofmaterial insoluble to the water-immiscible liquid and having a densitygreater than the density of the water. The density of this material isat least 1.1 times as great as the density of the water. In addition tobeing heavy, the objects forming the pile have sufficient strength andsize relation to create a pile having highly conductive voids comprisinga bulk porosity of at least thirty percent under the operatingconditions hereinafter set forth.

Preferably, the objects for forming the pile are transported by Watertransportation to the location for the pile and the pile is formed bydepositing the transported objects on the bottom of the body of water orlower barrier 19, and that portion of the objects previously de positedto form a mound or a truncated pyramid or coni cal structure. Use ofspecially transported objects is in contrast to merely dredging a pilemade up of mud or sand from the ocean floor or to merely blastingportions of rock on the ocean floor to form the pile. It is by watertransporting select material that a truly high bulk porosity pile ofstrong objects is formed in a uniform, structurally sound arrangement.Dredged mud or sand would be totally unsuitable for this purpose asthese materials would compact under load and form low conductivity porespaces. The most readily available and suitable objects for the pile arelarge rocks without fines having a minimum cross-sectional dimension ofat least 0.5 foot with fairly uniform rocks between 1 and 2 feet orlarger in size being preferred. Oyster shells without a large amount offines would also provide an excellent material for forming the pile. Byway of example, a half million barrel, truncated pyramid rock pilestorage with walls having a 3 to 1 slope and 50 feet high would have abase of 550 feet and and a top 250- feet wide. An '80 foot high pile ofthe same storage volume would have a 533 foot base and a 53 foot top. A2.5 million barrel pile 50 feet high would have a base of 1065 feet anda top of 765 feet.

It is advantageous to form the pile using transported objects and form aseries of first layers of small sized rocky objects 25, such as gravel,sand or clay on lower barrier 19 to act as a cushioning and protectivelayer for the lower barrier as shown in FIGURE 3. A heap of larger sizedrocky objects 27 are then formed on the series of first layers of smallsized rocky objects. This heap of larger sized rocky objects forms mostof the bulk of pile. A series of second layers of small sized rockyobjects 29 is formed over the heap of larger sized rocky objects. Thesecond series of layers forms the sea side rim of the pile and isespecially suited for completion of the storage reservoir as hereinaftershown. Second series of small objects 29 smooth the contours of thelarge objects, provide a protective layer of small objects, act asfilter bed and may provide a filler aggregate for the cover for thepile.

As will hereinafter be made more clear, the objects provide highlyconductive voids which are the storage volume, support the seal andstorage reservoir from all downward and inward forces, give weight tothe storage system, act as a structure on which a seal may be formed andas a filter bed and filter strengthening material for assisting insealing the sea side rim of the pile, provide self-adjusting support forthe seal allowing for variations in the sea bottom, and provide a way ofconsolidating the storage system.

After pile 11 is formed, there is formed thick upper barrier 31 whichcovers the pile, that is, the upper barrier spreads over the top of thepile and extends down on all sides of the pile and outward onto bottom13 of the body of water or lower barrier 19 thereby forming an invertedcontainer whose bottom rim will seal against the ocean floor or thelower barrier. The top of the upper barrier is below surface 17 of thebody of water so that the pressure inside the storage system may belowered without operating the storage reservoir under a vacuum or at apressure less than the vapor pressure of the oil. Upper barrier 31 mustalso be supported by the objects in pile 11. The objects directly underand in contact with the upper barrier provide a highly wave resistantstructure with many ways to increase the strength of the storagereservoir, to overcome cyclic forces and to control and repair leaks.The upper barrier is sufficiently impermeable to contain oil within thepile. Upper barrier 31 will be at least three inches thick with athickness at least as great as one foot being preferred. As illustratedin FIGURE 2, much greater thicknesses are contemplated. The upperbarrier is of suificient thickness to permit the pile covering seal totake the shape of the supporting pile.

The upper barrier may be composed of many different materials with orwithout reinforcing and any number of layers, provided that the barrierforms a strong. thick, longlasting seal over and supported by theobjects in the pile. The upper barrier needs to be much more rugged thanthe lower barrier and should maintain its properties for periods of fromten to thirty years. It is highly advantageous and essential to someembodiments hereof that the barriers, especially the upper barrier, bemoldable. A moldable barrier is readily deformed without rupture and isflexible, or pliable and resilient enough to fit the contours of theobjects in the pile or the contours of the sea floor and be readilysupported thereby. This elastic or deformable behavior incontradistinction to nondeforrnable or rigid barriers, such as cementaggregates or thick steel sheet, readily transfers forces through thebarrier to the support structure thereby compensating for pressuredifferentials, cyclic forces, periodic thrusts, uneven compaction ofsupport structure, and voids in the support structure adjacent eitherside of the barrier. The support structure for the lower barrier will bethe sea floor on one side and the objects in the pile on the other side.The support structure for the upper barrier will be the objects in thepile and the lower barrier or sea fioor around the outer rim of thepile. If a heavy material is placed on the upper barrier, this materialmay act as support structure against the buoyant force on the upperbarrier created by oil in the pile. The principal advantages of thismethod of constructing and operating the storage reservoir areobtainable because of the tihck, moldable character of the upper barrierand the way that the barrier is loaded and supported. A moldable upperbarrier is particularly suitable to compaction and consolidation of thepile to increase the stability of the reservoir and improve the sealbetween the upper and lower barriers.

Preferably, the upper barrier is composed of a series of separatelyformed layers. This laminated construction of layers superimposed on oneanother provides a more flexible load-supporting barrier withself-healing, lea-k preventive properties. A laminated construction alsopermits an optimum combination of materials of dilferent costs andproperties.

The upper barrier will be composed of oil insoluble materials that willform a strong, thick cover that is suitable for being supported by looseobjects in the pile and that possesses resistance to erosion, light,oxidation, age hardening, plant and marine growth, and flow at highangles of repose. Usually, these materials will be selected from thegroup consisting of pourable time-setting materials or flexible sheets,or mixtures thereof. Suitable sheets are the thick, strong plastic orneoprene film materials used in lining water disposal tanks in oilproduction areas. These liners have been readily joined under water. Forexample, an excellent sheet material that has been used in water is aneoprene sheet having a thickness of oneeighth to three-sixteenths of aninch, with a specific gravity of 1.4 to 1.5, tensile strength of about2,000 psi. and an elongation of 300 to 400 percent. Examples of pourablematerials are asphalts and special Portland cements.

Asphalts with or without fillers or reinforcing provide a universallyavailable pliable and resilient material which has been extensivelytested and developed for paving and marine uses such as lining canalsand preventing soil erosion. For a fuller discussion of techniques andmaterials, refer to Bitumen in Hydraulic Engineering, Baron W. F. vanAsbeck, volume Il, 1964, Elsevier Publishing Company, Library ofCongress Catalog Card Number 56- 3649, especially at pages 15, 70, and89. These asphalt lining materials are available in both prefabricatedand pourable forms. Asphalts are readily mixed with resins,plasticizers, fillers, aggregate, solubilizers, adhesives, wettingagents, and the like, to improve desirable properties such as adhesion,cohesion, plasticity, chemical and oxidation resistance, reducedshrinkage, resistance to age hardening, and the like. Asphalts have thefurther advantage of being already available in penetrating,time-setting mixtures which can be used to penetrate the ocean floor orlayers of objects in the pile. In this manner, a very thick, strong andheavy upper barrier may be formed. The

drawings show the upper and lower barriers formed with penetratingasphalt.

As shown in FIGURE 1, heavy material 33, which is heavier than water, isspread or distributed over the sea side or top of upper barrier 31. Itis preferred that this heavy material be formed by placing over theupper barrier a series of layers of small sized heavy material 35 to actas a cushioning and protective layer covering the upper barrier and as afilter bed for repairing leaks. A series of layers of large sized heavymaterial 37 is then placed over the series of layers of said small sizedmaterial. Preferably, the large and small sized materials will beobjects like those used in forming the pile. Heav material 33 functionsas a protective covering for the upper barrier, as support for the upperbarrier when the oil in the pile pushes upward against the upperbarrier, as a material for placing a net downward force on the upperbarrier and as a filter bed or protective cover for repairing leaks.When heavy material 33 is used to place a net downward force over theupper barrier, the amount of heavy material spread over the upperbarrier will counteract buoyant forces and be essentially proportionalto the amount of oil stored in the pile.

Emplaced in the pile are at least two fiow conduits. These flow conduitsmay be placed in location at any stage of construction of the storagesystem, that is, either before or after the pile, the upper barrier orheavy material 33 are formed. For example, the flow conduits could bethe legs of a platform or piling about which the pile is formed. Theflow conduits are made in a manner such that the flow conduits extendfrom inside pile 11 to outside the storage reservoir or to the sea sideof upper bar rier 31 and are adapted for alternately adding or removingoil and sea water from the pile.

There are many well-established Ways to accomplish placement andconnection to the flow conduits. One way is shown in FIGURE 1 whereinfirst flow conduit 39 is in communication with upper portion 21 of pile11 and extends upward to platform 41 with which the storage reservoirWill normally be associated and which may be separate from or a part ofthe storage pile. This platform will normally carry support equipmentand perhaps several wellheads which are not shown. Second flow conduit43 is in communication with lower portion 23 and extends upward to theplatform. First flow conduit 39 is comprised of oil inlet 45 and oiloutlet 47. Oil outlet 47 is connected to pump 49. With this arrangement,oil may be pumped into inlet 45 to the pile and may be removed from thepile by way of pump 49 and outlet 47. Second flow conduit 43 iscomprised of sea water inlet 51 and sea water outlet 53. Sea Wateroutlet 53 is connected to pump 55. Sea water inlet 51 has sea water dumpvalve 57 which is below surface 17 of the water and which when openedallows water to flow into the pile. This arrangement allows sea water tobe added to or removed from pile 11 wherever desired as hereinafter setforth. For example, when oil is being removed by way of oil outlet 47,sea water is allowed to flow by way of sea water inlet 51 into the pile.In a similar manner, sea water is removed from the pile by way of pump55 and sea water outlet 53 when oil is added to the pile.

FIGURE 3 shows a second and special arrangement for the flow conduitswhich is designed to maintain a reduced pressure inside the rock pilewhen oil is being stored in the pile. The purpose of this arrangementwill hereinafter be discussed in detail. In FIGURE 3, second flowconduit 43, which extends up to the platform is comprised of sea waterinlet-outlet 59 and gas lift inlet 61. Sea water is either added to orremoved from the pile by way of sea water inlet-outlet 59. In sea waterinlet-outlet 59 is sea water inlet valve 63 which is below surface 17 ofthe water, sea water outlet 65 which is above water surface 17. Gas liftinlet 61 has gas valve 67 and extends downward to the pile. Sea waterinlet valve 63 and gas valve 67 will in standard fashion be operableautomatically 75 and be connected through suitable means (not shown) tooil level sensor 69 which is placed in oil inlet at a level below watersurface 17. Oil level sensor 69 is any type of well-known liquid levelsensor and will not be described in detail. Similarly, the oil levelsensor is adapted in the usual manner to open and close gas valve 67 andsea water inlet valve 63 thereby controlling upper level 71 of the oilin oil inlet 45 to a level at water surface 17 or below water surface17.

Before any oil is placed in the pile, it would be best to compact thestorage pile and sea floor to its most stable arrangement and to testthe upper barrier for leaks. This can readily be accomplished byremoving water from the pile at a rate sufficient to reduce the pressureinside the pile when the barrier is impermeable. This may be done afterthe upper barrier is formed, but it will frequently be preferred toperform this step after only a portion of the upper barrier is formedand while this portion is still moldable. This step is carried out byremoving water from the pile by way of either or both of the flowconduits. If the upper barrier leaks water into the pile, the relationbetween the rate of water removal and pressure inside and outside thepile will indicate the size of the leak. The inward flow of waterthrough the upper barrier can readily be detected and located from theexterior or sea side of the upper barrier. The leak is readily repairedby either increasing the overall thickness of the upper barrier or byplugging the leak or leaks. The upper barrier or the pile of objectsunder the upper barrier, especially the small sized layers of rockyobjects, readily act as a filter bed upon which bridging and sealingmaterials may be screened out. The same techniques used in pluggingzones of lost circulation during Well drilling, or in plugging porous orfractured formations, may be used. When the barriers are sufficientlyimpermeable to allow the pressure inside the pile to be reduced to alevel below the pressure on the sea side of the upper barrier, thepressure differential across the large area of the barrier creates alarge inward and downward force on the pile. A downward force isrequired and this is one reason why the pile must rest on the lowerbarrier or the ocean floor. This force compacts the sea floor and thepile of objects to a very stable position. This force also causes themoldable barrier to snugly conform to the contour of the pile and fillvoids just below the upper barrier. Both of these results greatlystrengthen the whole system. Under certain conditions it may bedesirable to dehydrate the sand in the sea floor and better stabilizethe foundation for the pile by performing the same step on the lowerbarrier before the pile is formed. In which case, the Water would bepumped from the sand below the lower barrier through either speciallylaid piping or through the legs of the platform. Usually this will notbe necessary since the large weight of the pile on the lower barriergreatly compacts the sea floor making the sea floor and the lowerbarrier impermeable and stable.

When operating the pile as an oil storage reservoir, thewater-immiscible oil is added to pile through first flow conduit 39 :byway of oil inlet 45 during a first period. The oil in the pile, beinglighter than water, collects in upper portion 21 just under upperbarrier 31. Whenever desired, a portion of the oil stored in the pile isremoved from the pile through first flow conduit 39 by way of oil outlet47 and pump 49. The voids in the pile are highly conductive so that oilmay be removed just as rapidly as if the storage reservoir were astandard oil tank. Since this is important, 1t should be apparent thatseveral flow conduits could be spaced about the storage reservoir ifneeded.

During the periods when oil is being removed from or added to the pile,sea water is added to or removed from the pile. Sea water may be removedfrom the pile when 011 is being added to the pile through second flowconduit 43 by way of pump and sea water outlet 53 or through second fiowconduit 43' by way of sea water inlet outlet 59 and sea water outlet byinjecting gas into gas lift inlet 61. Removing Water as oil is addedprevents overpressurization of the pile and allows the oil to beproduced into the pile by gravity flow from above water separators orother production equipment if desired. In a similar manner, when oil isbeing removed from the pile, sea water may be added to the pile throughsecond flow conduit 43 by way of sea water inlet 51 and sea Water dumpvalve 57 or through second flow conduit 43 by Way of sea water inletvalve 63 and sea water inlet-outlet 59.

It has been pointed out that it is advantageous to place a net inwardand downward force on the exterior or sea side of the upper barrier. Dueto the way that the storage system is constructed, the uniquerelationship between the upper barrier and pile and the location ofthese in relation to the surface and bottom of the water, this force isreadily created and transmitted from the upper barrier to the objectsbelow this upper barrier without collapsing the storage system. Theadvantages derived from being able to place a large net inward force onthe upper barrier without damaging or collapsing the storage system orgreatly altering the storage volume are many. For example, this permitsthe operator to lower the pressure inside the storage pile andstrengthen and anchor the pile against peak wave forces and to providestable tanker mooring or a firm foundation for loading or productionequipment. Reducing the pressure also provides a way of repairing leaksfrom the exterior of the reservoir and of preventing leakage of thelighter-than-water, stored liquid into the surrounding water.

One way to accomplish a net, but permanent and costly, downward force isto spread heavy material 33 over upper barrier 31 as shown in FIGURE 1.The amount of heavy material spread over the upper barrier is sufiicientto create a downward force on the upper barrier greater than the upwardforce on the upper barrier created by the waterimmiscible being lighterthan water. The amount and distribution of heavy material required to atleast balance this buoyant force is readily calculated from suchinformation as the depth of the upper barrier below water surface 17,the specific gravities and densities of the oil and water and the volumeof oil to be placed in the pile. The amount of heavy material spreadover the upper barrier will be substantially greater than the minimumamount necessary to counteract the buoyancy of the oil.

An especially advantageous way for placing a net downward force on theupper barrier is to create a pressure differential across the upperbarrier by reducing the pressure inside the pile to a level below thewater pressure on the sea side or exterior side of the upper barrier.This way of creating the desired force has the advantages of beingreadily adjusted to varying conditions, of creating a truly inward forceas well as a downward force, of improving the seal between the rim ofthe upper barrier and the sea floor or lower barrier, of preventingleakage of oil into the water, of assisting in repairing leaks, of beingless costly than other methods and other similar advantages. Thepressure inside the pile may be reduced without creating a vacuum oroperating the pile below the vapor pressure of the oil because thebarrier is below the surface of the water. This pressure reductionplaces a large inward, downward force on the storage system. Thus, afterthe storage reservoir has been formed and oil added to the pile, thepressure inside the reservoir may be reduced for any predeterminedperiod whenever desired. For example, the pressure inside the pile maybe reduced to strengthen and anchor the reservoir against peak waveforces, to provide stable tanker mooring or a firm foundation for otherequipment or a platform, and to repair or prevent leaks. This pressurereduction may be readily accomplished by removing sea water from thepile using techniques previously mentioned.

It will also be advantageous in some instances to use a combination ofheavy material spread over the upper barrier and a lower pressure insidethe pile. The heavy material acts as a protective layer over thebarrier, or as a 1O safety control in the event that control of thelower pressure inside the pile is lost, or as a support structureagainst upward rupture of the upper barrier, or a combination of thesefunctions.

It is advantageous to reduce the pressure inside the pile throughout thefirst period when oil is being added to the pile. One method ofaccomplishing this is shown in FIGURE 3. During the first period whenoil is being added to the pile by way of oil inlet 45, oil level sensor69 is used to determine upper oil level 71 of the oil in the oil inlet.This upper level of oil is maintained at a level at least as low assurface 17 of body of water 15, and will usually be maintainedsubstantially below surface 17. As illustrated, this is accomplished byusing oil level sensor 69 to open gas valve 67 whenever the upper levelof the oil rises above a predetermined level. When gas valve 67 opens,gas lift gas passes through gas lift inlet 61 and lifts sea Water out ofthe pile by way of sea water inlet-outlet 59 and sea water outlet 65.The rate of seawater removal is such that upper oil level 71 does notrise above the surface of the water. The oil level sensor may also beused to shut off production of oil when necessary. For example, it maybe necessary to stop production if a leak develops and the oil levelrises above a preset level. Under these conditions, the pressure insidethe pile is maintained below the pressure on the exterior or sea side ofthe upper barrier because the oil is lighter than water and the head ofwater is either equal to or greater than the head of oil.

When the pressure inside the pile is to be maintained below the waterpressure on the sea side of the upper barrier during oil removal fromthe pile, oil level sensor 69 controls the rate of sea water entrancethrough sea water inlet valve 63. In a similar manner, the pressureinside the pile may be maintained below the water pressure on the seaside of the upper barrier throughout the periods when oil is being addedto, stored in and removed from the pile. Oil level sensor 69 may be usedto open and close gas valve 67 and sea water inlet valve 63 so thatupper oil level 71 stays relatively constant for any preset period.

Certain modifications of the invention will be apparent to those skilledin this art. For example, what is illustrated'in one figure could havebeen placed in the other figures. A pressure sensing system could beused in place of a liquid level sensing system for maintaining a lowerpressure in the pile. Any form of pump suitable for removing liquidsfrom the pile could be used in place of the gas lift system of FIGURE 3.A material heavier than water could be placed on the sea floor ahead ofthe lower barrier or as a part of forming the lower barrier. The flowconduits for adding and removing oil and for adding and removing watercould be in one or more pipes and a series of pipes could be spreadabout the pile to provide for uniform pressures and to prevent anypossibility of water coning. The pipes could be the legs of theplatform. The illustrative details disclosed are therefore not to beconstrued as imposing unnecessary limitations on the invention.

What is claimed is:

1. An underwater storage method for a water-immiscible liquid having aspecific gravity less than said water, which method comprises forming apile on the bottom of a body of water with the top of said pile beingbelow the surface of said body of water, said pile being composed of aquantity of objects heaped together in multiple horizontal and verticallayers thereby providing a pile having an upper portion and a lowerportion, said objects being composed of material having a densitygreater than the density of said water, forming a thick upper barriercovering said pile and supported by said objects in said pile, saidupper barrier being sufficiently impermeable to contain saidwater-immiscible liquid within said pile, and at some time duringconstruction of said storage placing first and second flow conduits in amanner such that when said storage is completed said flow conduitsextend from inside said pile to outside said upper barrier with saidfirst flow conduit in communication with said upper portion of said pileand said second fiow conduit in communication with said lower portion ofsaid pile.

2. The method of claim 1 wherein a material heavier than water is spreadover the exterior of said upper barrier.

3. The method of claim 1 wherein the method includes the steps of addingthe water-immiscible liquid to said pile during a first period, andthereafter removing a portion of said water-immiscible liquid from saidpile.

4. The method of claim 3 wherein the method includes the steps ofremoving water from said pile at the same time as Said water-immiscibleliquid is added to said pile and adding water to said pile at the sametime as said portion of said water-immiscible liquid is removed fromsaid pile.

5. The method of claim 4 wherein during said first period thewater-immiscible liquid is added by way of said first flow conduit andthe method includes the steps of determining the upper level of saidwater-immiscible liquid in said first flow conduit and maintaining saidupper lever of said water-immiscible liquid at level at least as low assaid surface of said body of water.

6. The method of claim 3 wherein for a predetermined period the pressureof said water-immiscible liquid in said pile is maintained at a pressurebelow the water pressure on the exterior of said upper barrier.

7. The method of claim 6 wherein the predetermined period extendsthroughout said first period.

8. The method of claim 6 wherein a material heavier than water is spreadover the exterior of said upper barmen 9. The method of claim 3 whereina material heavier than water is spread over the exterior of said upperbarrier, the amount of said material being sufificient to create adownward force on said upper barrier greater than the upward force onsaid upper barrier created by said waterimmiscible liquid being lighterthan said water.

10. The method of claim 1 wherein after at least a portion of said upperbarrier is formed, water is removed from said pile at a rate sufiicientto reduce the pressure inside said pile.

11. The method of claim 1 wherein the objects for construc ion of saidpile are transported by water transportation to the location for saidpile and said pile is formed by depositing said transported objects onthe bottom of the body of water and that portion of said objectspreviously deposited.

12. The method of claim 11 wherein a material heavier than water isspread over the exterior of said upper barrier.

13. The method of claim 11 wherein the method includes the steps ofadding the water-immiscible liquid to said pile during a first period,and thereafter removing a portion of said water-immiscible liquid fromsaid pile.

14. The method of claim 13 wherein the method includes the steps ofremoving water from said pile at the same time as said water-immiscibleliquid is added to said pile and adding water to said pile at the sametime as said portion of said water-immiscible liquid is removed fromsaid pile.

15. The method of claim 14 wherein during said first period thewater-immiscible liquid is added by way of said first flow conduit andthe method includes the steps of determining the upper level of saidwater-immiscible liquid in said first flow conduit and maintaining saidupper level of said water-immiscible liquid at level at least as low assaid surface of said body of water.

16. The method of claim 13 wherein for a predetermined period thepressure of said water-immiscible liquid in said pile is maintained at apressure below the water pressure on the exterior of the upper barrier.

17. The method of claim 16 wherein the predetermined period extendsthroughout said first period.

18. The method of claim 16 wherein a material heavier than water isspread over the exterior of said upper barner.

19. The method of claim 13 wherein a material heavier than water isspread over the exterior of said upper barrier, the amount of saidmaterial being sufficient to create a downward force on said upperbarrier greater than the upward force on said upper barrier created bysaid waterimmiscible liquid being lighter than said water.

20. The method of claim 11 wherein after at least a portion of saidupper barrier is formed, water is removed from said pile at a ratesufiicient to reduce the pressure inside said pile.

21. The method of claim 11 wherein a major portion of said objectsforming said pile is composed of large rocks having a minimumcross-sectional dimension of at least 0.5 foot.

22. The method of claim 11 wherein a major portion of said objectsforming said pile is composed of oyster shells.

23. The method of claim 11 wherein the pile is formed by forming aseries of first layers of small sized rocky objects on the bottom of thebody of water, forming a heap of larger sized rocky objects on saidfirst layers of said small sized rocky objects, and forming a series ofsecond layers of small sized rocky objects over said heap of said largersized rockv objects.

24. The method of claim 23 wherein after the upper barrier is formed,there is placed over said upper barrier a series of layers of smallsized material and a series of layers of large sized material is placedover said series of layers of said small sized material, said smallsized material and said large sized material being heavier than water.

25. The method of claim 11 wherein before the pile is formed, there isformed a lower barrier covering a portion of the bottom of the body ofwater and the pile is formed on top of said lower barrier, said lowerbarrier being designed to be substantially impermeable.

26. The method of claim 25 wherein a material heavier than water isspread over the exterior of said upper barrier.

27. The method of claim 25 wherein the method includes the steps ofadding the Water-immiscible liquid to said pile during a first period,and thereafter removing a portion of said water-immiscible liquid fromsaid pile.

28. The method of claim 27 wherein the method includes the steps ofremoving water from said pile at the same time as said water-immiscibleliquid is added to said pile and adding water to said pile at the sametime as said portion of said water-immiscible liquid is removed fromsaid pile.

29. The method of claim 28 wherein during said first period thewater-immiscible liquid is added by way of said first flow conduit andthe method includes the steps of determining the upper level of saidwater-immiscible liquid in said first flow conduit and maintaining saidupper level of said water-immiscible liquid at level at least as low assaid surface of said body of water.

30. The method of claim 27 wherein for a predetermined period thepressure of said water-immiscible liquid in said pile is maintained at apressure below the water pressure on the exterior of the upper barrier.

31. The method of claim 30 wherein the predetermined period extendsthroughout said first period.

32. The method of claim 30 wherein a material heavier than water isspread over the exterior of said upper barrier.

33. The method of claim 27 wherein a material heavier than water isspread over the exterior of said upper barrier, the amount of saidmaterial being sufiicient to create a downward force on said upperbarrier greater than the upward force on said upper barrier created bysaid waterimmiscible liquid being lighter than said water.

34. The method of claim 25 wherein after at least a portion of saidupper barrier is formed, water is removed from said pile at a ratesufficient to reduce the pressure inside said pile.

35. The method of claim 25 wherein a substantial portion of saidmaterial forming said pile is composed of large rocks having a minimumcross-sectional dimension of at least 0.5 foot.

36. The method of claim 25 wherein a major portion of said objectsforming said pile is composed of oyster shells.

37. The method of claim 25 wherein the pile is formed by forming aseries of first layers of small sized rocky objects on the lower barriercovering a portion of the body of water, forming a heap of larger sizedrocky objects on said first layers of said small sized rocky objects andforming a second series of layers of said small sized rocky objects oversaid heap of said larger sized rocky objects.

38. The method of claim 37 wherein after at least a portion of saidupper barrier is formed, water is removed from said pile at a ratesufiicient to reduce the pressure inside said pile.

39. The method of claim 37 wherein after the upper barrier is formed,there is placed over said upper barrier a series of layers of smallsized material and a series of layers of large sized material is placedover said series of layers of said small sized material, said smallsized material and said large sized material being heavier than water.

References Cited UNITED STATES PATENTS 2,536,320 1/1951 Smith 61-.5 X2,747,774 5/ 1956 Breitenbach 6l.5 X 2,879,646 3/ 1959 Brandt 61-.53,003,322 10/1961 Jordan 61-.5 3,068,654 12/ 1962 Warren 61.5 3,113,69910/ 1963 Crawford et a1. 3,152,640 10/ 1964 Marx 6l-.5 X

FOREIGN PATENTS 769,764 3/ 1957 Great Britain.

EARL J. WITMER, Primary Examiner.

US. Cl. X.R. 6 1-1

